1. Field of the Invention
The present invention relates to a failure diagnosis apparatus for an exhaust pressure sensor which detects an exhaust pressure of an internal combustion engine.
2. Description of the Related Art
Japanese Patent Laid-open No. H06-167236 (JP-'236) discloses a failure detecting apparatus for detecting a failure of a pressure sensor which detects a pressure in an exhaust gas recirculation passage of an internal combustion engine. According to this apparatus, it is determined that the pressure sensor has failed if a difference between the pressure in the passage detected by the pressure sensor and the atmospheric pressure is less than the predetermined value in the closed state of an exhaust gas recirculation control valve which opens and closes the exhaust gas recirculation passage.
The above-described conventional apparatus can detect a stuck failure caused by freeze of the pressure sensor when the output of the pressure sensor indicates a value of a pressure in the vicinity of the atmospheric pressure. However, it is impossible to detect a stuck failure caused when the pressure sensor indicates a value of a pressure which is higher than the atmospheric pressure by the predetermined value (i.e., the difference between the detected pressure and the atmospheric pressure is greater than the predetermined value). Therefore, there is a possibility of an erroneous determination that the pressure sensor may be normal, although the pressure sensor has actually failed.